This invention relates to a multicolor luminescent device, especially to a multicolor luminescent device suitable for use in public and industrial indicators, color displays, and the like.
Electronic display devices which are generally called man machine interfaces transfer a variety of information from various machines to man via the organ of vision. The electronic display devices play an important role as interfaces linking man with machines.
There are an active type (light emitting type) and a passive type (light accepting type) for such electronic display devices. The active type includes, for example, a CRT (Cathode Ray Tube), PDP (Plasma Display Panel), ELD (Electro Luminance Display), VFD (Vacuum Fluorescent Display), and LED (Light Emitting Diode). On the other hand, the passive type includes, for example, an LCD (Liquid Crystal Display), ECD (Electro Chemical display), EPID (Electro Phoretic Image Display), SPD (Suspended Particle Display), TBD (Twisting Ball Display), and PLZT (Transparent Ceramics Display, transparent ferroelectric PLZT ((Pb, La) (Zr, Ti)O.sub.3 ceramic display).
Among these displays, the ELD is characterized in exhibiting high visibility due to self-emission and in having excellent impact resistance because of being completely a solid. At present, the development of variable ELDs using an inorganic or an organic compound as the emitting layer is being advanced. Especially, an organic ELD (or organic EL element) in which an organic compound is sandwiched between two electrodes is notable because it can use many sorts of organic compounds and efficiently emit a highly intensive light with a variety of colors.
The methods for preparing a full-color organic ELD include, for example, a method for separately positioning emitting parts of the organic EL elements on the same flat and emitting light with different colors, e.g. three primary colors, that is, red, blue, and green; and a method for separating or converting a monocromatic light using color conversion layers, e.g. a color filter or a fluorescent material.
However, it is necessary to exploit luminous materials of different colors for emitting lights of different colors, thereby providing multiple colors. There is also the problem of inferior durability in a process, for example, photolithography, for separately positioning the emitting parts of the organic EL elements on the same flat. In contrast, the latter method for separating or converting the monocromatic light using the color conversion layers is excellent and simple since it is only provided with a layer emitting a monocromatic color as the emitting layer.
However, because the color conversion layers are provided in addition to the organic EL elements in the latter method, gaps are made between the organic EL elements and the color conversion layers and also between the color conversion layers. These gaps cause light leakage from the organic EL elements and the color conversion layers so that the angle of view is narrowed (the phenomenon of color drift). Therefore, by this method, only a multicolor luminescent device with degraded visibility can be provided.
For this, disclosed is a method in which a transparent resin layer is provided between EL elements and color filters and the thickness of the transparent resin layer is less than the interval between pixels of the EL elements as shown in FIG. 15 (see Japanese Patent Application Laid-open No. 94878/1993).
However, there is no shielding layer in this structure. Light leakage from the side surface of the color filter layers is not prevented so that the problem of angle of view is insufficiently solved. Also, even if, for example, a fluorescent material is used instead of the color filter layers, it emits a fluorescent light more isotropically. As a result, light leakage is increased, thereby impairing the visibility.
Further, a multicolor luminescent device in which fluorescent media are arranged to accept the emitting light from the organic EL elements is disclosed (see Japanese Patent Application Laid-open No. 258860/1993). However, no light-shielding layer positioned between the fluorescent media is disclosed, as shown in FIG. 16. Therefore, the problem of angle of view is insufficiently solved by this method.
In addition, an EL panel is disclosed wherein spacers having a light-shielding capability and projecting almost vertically to the substrate surface of EL elements are disposed in the clearances between pixels of the EL elements while color filters face EL elements as shown in FIG. 17 (see Japanese Patent Application Laid-open NO. 94879/1993).
In this case, the problem of angle of view is solved, but the relation between the thickness of the light shielding layer and the thickness of the color conversion layer is not clearly disclosed. Also, the relation between the distance between the organic EL element and the shielding layer and the width of the shielding layer is not clearly disclosed. Therefore, a substantially full-color ELD cannot be manufactured.
Also, as shown in FIG. 18, a color display in which EL elements and color filters are facing each other is disclosed (see Japanese Patent Application Laid-open No. 40888/1988). However, there is no clear disclosure of the relation between the thickness of the light shielding layer and the thickness of the color conversion layer, and also there is no clear disclosure of the relation between the distance from the organic EL elements to the shielding layer and the width of the shielding layer in the same way as the above method. Therefore, a substantially full-color ELD cannot be manufactured.
This invention has been achieved in view of this situation and has an object of providing a multicolor luminescent device which has excellent characteristics in the angle of view, is capable of inhibiting the occurrence of color drift (color mixing), and has excellent visibility and practical use.